1. Technical Field
The present invention generally relates to a method and apparatus for cleaning atmosphere gas adapted to make high-purity fine particles of reactive metals. More particularly, it relates to a method of removing moisture remaining in the atmosphere gas in a trace amount to an extremely low content level in manufacturing high-purity fine particles of reactive metals, the metals being reactive especially in terms of liability to forming hydroxides (the "reactive metals," e.g., metal of IIa, IIIa, IVa and IVb families in the periodical table), as well as to an apparatus for generating Na vapor to be used in the gas cleaning step and to a method and apparatus for detecting a trace amount of moisture thereafter.
2. Background Art
In treating reactive metals generally, the practice of providing an inert or vacuum environment to which the metals are exposed is known in the art.
In connection with treating reactive metals, there is presently a strong need for manufacturing high-purity fine particles, especially those which are apt to form hydroxides (e.g., the IIa, IIIa, IVa and IV b family metals in the periodical table, hereinafter referred to as "reactive metals") from a sector of advanced material such as superconducting materials. Here, one technical problem is that an ordinary inert gas atmosphere or vacuum is not good enough for the reactive metals, because they form hydroxides upon reaction with moisture remaining in the environment gas even if the moisture exists in a small amount and the hydroxides give rise to voids or other defects in the product particles, thereby degrading the qualities thereof.
For removing moisture from the atmosphere gas so as to prevent the above defects, the presently common practice is either to use a moisture absorbent such as silica gel, sulfuric acid, sodium hydroxide or anhydrous magnesium perchlorate, or to use a dehumidifying machine of one sort or another. However, these methods are not completely capable of removing the moisture to an extremely low content level (e.g., 10-100 Weight/Volume part per billion (W/V ppb)) that satisfies us in making high-purity fine particles of reactive metals.
With the methods using a moisture absorbent moreover, there is a problem of the absorbent releasing the moisture it has captured once, if the atmospheric temperature rises or the pressure drops.
Even if such a low moisture content has been attained, furthermore, there exists no method today to easily and qualitatively detect moisture present in such trace amount. That is to say, today's general practice is to sample out the atmosphere gas and determine the moisture content by letting the absorber (usually calcium chloride) absorb its moisture away and knowing the absorber's weight difference, i.e., the so-called absorbed mass method; but this method is in applicable to certain usages because of sheer lack of sensitivity.
Furthermore, this method is inapplicable where manufacturing of the reactive metals is always conducted in a small-size hermetically enclosed vessel, and the absorbed mass method cannot be practices in such a confined space.